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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2012 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: PersistentObject.Snapshot.html 947 2014-11-12 22:14:09Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.pobj;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.io.BufferedInputStream;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.io.BufferedOutputStream;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.io.File;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.io.FileInputStream;<a name="line.13"></a>
<span class="sourceLineNo">014</span>import java.io.FileOutputStream;<a name="line.14"></a>
<span class="sourceLineNo">015</span>import java.io.IOException;<a name="line.15"></a>
<span class="sourceLineNo">016</span>import java.io.InputStream;<a name="line.16"></a>
<span class="sourceLineNo">017</span>import java.io.OutputStream;<a name="line.17"></a>
<span class="sourceLineNo">018</span>import java.util.ArrayList;<a name="line.18"></a>
<span class="sourceLineNo">019</span>import java.util.HashSet;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import java.util.Set;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import java.util.concurrent.ExecutorService;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import java.util.concurrent.Executors;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.util.concurrent.ScheduledExecutorService;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.util.concurrent.ScheduledFuture;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.util.concurrent.TimeUnit;<a name="line.25"></a>
<span class="sourceLineNo">026</span><a name="line.26"></a>
<span class="sourceLineNo">027</span>import javax.validation.ConstraintViolation;<a name="line.27"></a>
<span class="sourceLineNo">028</span>import javax.xml.transform.Result;<a name="line.28"></a>
<span class="sourceLineNo">029</span>import javax.xml.transform.Source;<a name="line.29"></a>
<span class="sourceLineNo">030</span>import javax.xml.transform.stream.StreamResult;<a name="line.30"></a>
<span class="sourceLineNo">031</span>import javax.xml.transform.stream.StreamSource;<a name="line.31"></a>
<span class="sourceLineNo">032</span><a name="line.32"></a>
<span class="sourceLineNo">033</span>import org.dellroad.stuff.io.AtomicUpdateFileOutputStream;<a name="line.33"></a>
<span class="sourceLineNo">034</span>import org.dellroad.stuff.io.FileStreamRepository;<a name="line.34"></a>
<span class="sourceLineNo">035</span>import org.slf4j.Logger;<a name="line.35"></a>
<span class="sourceLineNo">036</span>import org.slf4j.LoggerFactory;<a name="line.36"></a>
<span class="sourceLineNo">037</span><a name="line.37"></a>
<span class="sourceLineNo">038</span>/**<a name="line.38"></a>
<span class="sourceLineNo">039</span> * Main class for Simple XML Persistence Objects (POBJ).<a name="line.39"></a>
<span class="sourceLineNo">040</span> *<a name="line.40"></a>
<span class="sourceLineNo">041</span> * &lt;h3&gt;Overview&lt;/h3&gt;<a name="line.41"></a>
<span class="sourceLineNo">042</span> *<a name="line.42"></a>
<span class="sourceLineNo">043</span> * &lt;p&gt;<a name="line.43"></a>
<span class="sourceLineNo">044</span> * A {@link PersistentObject} instance manages an in-memory database with ACID semantics and strict validation that is<a name="line.44"></a>
<span class="sourceLineNo">045</span> * represented by a regular Java object graph (i.e., a root Java object and all of the other objects that it (indirectly)<a name="line.45"></a>
<span class="sourceLineNo">046</span> * references). The object graph can be (de)serialized to/from XML, and this XML representation is used for persistence<a name="line.46"></a>
<span class="sourceLineNo">047</span> * in the file system. The backing XML file is read in at initialization time and updated after each change.<a name="line.47"></a>
<span class="sourceLineNo">048</span> * &lt;/p&gt;<a name="line.48"></a>
<span class="sourceLineNo">049</span> *<a name="line.49"></a>
<span class="sourceLineNo">050</span> * &lt;p&gt;<a name="line.50"></a>
<span class="sourceLineNo">051</span> * All changes required copying the entire object graph, and are atomic and strictly serialized. In other words, the<a name="line.51"></a>
<span class="sourceLineNo">052</span> * entire object graph is read and written by value. On the filesystem, the persistent XML file<a name="line.52"></a>
<span class="sourceLineNo">053</span> * is updated by writing out a new, temporary copy and renaming the copy onto the original, using {@link File#renameTo<a name="line.53"></a>
<span class="sourceLineNo">054</span> * File.renameTo()} so that changes are also atomic from a filesystem perspective, i.e., it's not possible to open an<a name="line.54"></a>
<span class="sourceLineNo">055</span> * invalid or partial XML file (assuming filesystem renames are atomic, e.g., all UNIX variants). This class also<a name="line.55"></a>
<span class="sourceLineNo">056</span> * supports information flowing in the other direction, where we pick up "out of band" updates to the XML file (see below).<a name="line.56"></a>
<span class="sourceLineNo">057</span> * &lt;/p&gt;<a name="line.57"></a>
<span class="sourceLineNo">058</span> *<a name="line.58"></a>
<span class="sourceLineNo">059</span> * &lt;p&gt;<a name="line.59"></a>
<span class="sourceLineNo">060</span> * This class is most appropriate for use with information that must be carefully controlled and validated,<a name="line.60"></a>
<span class="sourceLineNo">061</span> * but that doesn't change frequently. Configuration information for an application stored in a {@code config.xml}<a name="line.61"></a>
<span class="sourceLineNo">062</span> * file is a typical use case; beans whose behavior is determined by the configured information can subclass<a name="line.62"></a>
<span class="sourceLineNo">063</span> * {@link AbstractConfiguredBean} and have their lifecycles managed automatically.<a name="line.63"></a>
<span class="sourceLineNo">064</span> * &lt;/p&gt;<a name="line.64"></a>
<span class="sourceLineNo">065</span> *<a name="line.65"></a>
<span class="sourceLineNo">066</span> * &lt;p&gt;<a name="line.66"></a>
<span class="sourceLineNo">067</span> * Because each change involves copying of the entire graph, an efficient graph copy operation is desirable.<a name="line.67"></a>
<span class="sourceLineNo">068</span> * The {@linkplain AbstractDelegate#copy default method} is to serialize and then deserialize the object graph<a name="line.68"></a>
<span class="sourceLineNo">069</span> * to/from XML in memory. See {@link org.dellroad.stuff.java.GraphCloneable} for a much more efficient approach.<a name="line.69"></a>
<span class="sourceLineNo">070</span> * &lt;/p&gt;<a name="line.70"></a>
<span class="sourceLineNo">071</span> *<a name="line.71"></a>
<span class="sourceLineNo">072</span> * &lt;h3&gt;Validation&lt;/h3&gt;<a name="line.72"></a>
<span class="sourceLineNo">073</span> *<a name="line.73"></a>
<span class="sourceLineNo">074</span> * &lt;p&gt;<a name="line.74"></a>
<span class="sourceLineNo">075</span> * Validation is peformed in Java (not in XML) and defined by the provided {@link PersistentObjectDelegate}. This delegate<a name="line.75"></a>
<span class="sourceLineNo">076</span> * guarantees that only a valid root Java object can be read or written. Setting an invalid Java root object via<a name="line.76"></a>
<span class="sourceLineNo">077</span> * {@link #setRoot setRoot()} with throw an exception; reading an invalid XML file on disk will generate<a name="line.77"></a>
<span class="sourceLineNo">078</span> * an error (or be ignored; see "Empty Starts" below).<a name="line.78"></a>
<span class="sourceLineNo">079</span> * &lt;/p&gt;<a name="line.79"></a>
<span class="sourceLineNo">080</span> *<a name="line.80"></a>
<span class="sourceLineNo">081</span> * &lt;h3&gt;Update Details&lt;/h3&gt;<a name="line.81"></a>
<span class="sourceLineNo">082</span> *<a name="line.82"></a>
<span class="sourceLineNo">083</span> * &lt;p&gt;<a name="line.83"></a>
<span class="sourceLineNo">084</span> * When the object graph is updated, it must pass validation checks, and then the persistent XML file is updated and<a name="line.84"></a>
<span class="sourceLineNo">085</span> * listener notifications are sent out. Listeners are always notified in a separate thread from the one that invoked<a name="line.85"></a>
<span class="sourceLineNo">086</span> * {@link #setRoot setRoot()}. Support for delayed write-back of the persistent XML file is included: this<a name="line.86"></a>
<span class="sourceLineNo">087</span> * allows modifications that occur in rapid succession to be consolidated into a single filesystem write operation.<a name="line.87"></a>
<span class="sourceLineNo">088</span> * &lt;/p&gt;<a name="line.88"></a>
<span class="sourceLineNo">089</span> *<a name="line.89"></a>
<span class="sourceLineNo">090</span> * &lt;p&gt;<a name="line.90"></a>
<span class="sourceLineNo">091</span> * Support for optimistic locking is included. There is a "current version" number which is incremented each<a name="line.91"></a>
<span class="sourceLineNo">092</span> * time the object graph is updated; writes may optionally specify this number to ensure no intervening changes<a name="line.92"></a>
<span class="sourceLineNo">093</span> * have occurred. If concurrent updates are expected, applications may choose to implement a 3-way merge algorithm<a name="line.93"></a>
<span class="sourceLineNo">094</span> * of some kind to handle optimistic locking failures.<a name="line.94"></a>
<span class="sourceLineNo">095</span> * &lt;/p&gt;<a name="line.95"></a>
<span class="sourceLineNo">096</span> *<a name="line.96"></a>
<span class="sourceLineNo">097</span> * &lt;p&gt;<a name="line.97"></a>
<span class="sourceLineNo">098</span> * To implement a truly atomic read-modify-write operation without the possibility of locking failure, simply<a name="line.98"></a>
<span class="sourceLineNo">099</span> * synchronize on this instance, e.g.:<a name="line.99"></a>
<span class="sourceLineNo">100</span> *  &lt;blockquote&gt;&lt;pre&gt;<a name="line.100"></a>
<span class="sourceLineNo">101</span> *  synchronized (pobj) {<a name="line.101"></a>
<span class="sourceLineNo">102</span> *      MyRoot root = pboj.getRoot();<a name="line.102"></a>
<span class="sourceLineNo">103</span> *      root.setFoobar("new value");    // or whatever else we want to modify<a name="line.103"></a>
<span class="sourceLineNo">104</span> *      pobj.setRoot(root);<a name="line.104"></a>
<span class="sourceLineNo">105</span> *  }<a name="line.105"></a>
<span class="sourceLineNo">106</span> *  &lt;/pre&gt;&lt;/blockquote&gt;<a name="line.106"></a>
<span class="sourceLineNo">107</span> * &lt;/p&gt;<a name="line.107"></a>
<span class="sourceLineNo">108</span> *<a name="line.108"></a>
<span class="sourceLineNo">109</span> * &lt;p&gt;<a name="line.109"></a>
<span class="sourceLineNo">110</span> * Instances can also be configured to automatically preserve one or more backup copies of the persistent file on systems that<a name="line.110"></a>
<span class="sourceLineNo">111</span> * support hard links (see {@link FileStreamRepository}). Set the {@link #getNumBackups numBackups} property to enable.<a name="line.111"></a>
<span class="sourceLineNo">112</span> * &lt;/p&gt;<a name="line.112"></a>
<span class="sourceLineNo">113</span> *<a name="line.113"></a>
<span class="sourceLineNo">114</span> * &lt;h3&gt;"Out-of-band" Writes&lt;/h3&gt;<a name="line.114"></a>
<span class="sourceLineNo">115</span> *<a name="line.115"></a>
<span class="sourceLineNo">116</span> * &lt;p&gt;<a name="line.116"></a>
<span class="sourceLineNo">117</span> * When a non-zero {@linkplain #getCheckInterval check interval} is configured, instances support "out-of-band" writes<a name="line.117"></a>
<span class="sourceLineNo">118</span> * directly to the XML persistent file by some other process. This can be handy in cases where the other process (perhaps hand<a name="line.118"></a>
<span class="sourceLineNo">119</span> * edits) is updating the persistent file and you want to have the running Java process pick up the changes just as if<a name="line.119"></a>
<span class="sourceLineNo">120</span> * {@link PersistentObject#setRoot setRoot()} had been invoked. In particular, instances will detect the appearance<a name="line.120"></a>
<span class="sourceLineNo">121</span> * of a newly appearing persistent file after has starting without one (see "empty starts" below). In all cases, persistent<a name="line.121"></a>
<span class="sourceLineNo">122</span> * objects must properly validate. To avoid reading a partial file the external process should write the file atomically by<a name="line.122"></a>
<span class="sourceLineNo">123</span> * creating a temporary file and renaming it; however, this race window is small and in any case the problem is self-correcting<a name="line.123"></a>
<span class="sourceLineNo">124</span> * because a partially written XML file will not validate, and so it will be ignored and retried after another<a name="line.124"></a>
<span class="sourceLineNo">125</span> * {@linkplain #getCheckInterval check interval} milliseconds has passed.<a name="line.125"></a>
<span class="sourceLineNo">126</span> * &lt;/p&gt;<a name="line.126"></a>
<span class="sourceLineNo">127</span> *<a name="line.127"></a>
<span class="sourceLineNo">128</span> * &lt;p&gt;<a name="line.128"></a>
<span class="sourceLineNo">129</span> * A special case of this is effected when {@link PersistentObject#setRoot setRoot()} is never explicitly invoked<a name="line.129"></a>
<span class="sourceLineNo">130</span> * by the application. Then some other process must be responsible for all database updates via XML file, and this class<a name="line.130"></a>
<span class="sourceLineNo">131</span> * will automatically pick them up, validate them, and send out notifications to listeners.<a name="line.131"></a>
<span class="sourceLineNo">132</span> * &lt;/p&gt;<a name="line.132"></a>
<span class="sourceLineNo">133</span> *<a name="line.133"></a>
<span class="sourceLineNo">134</span> * &lt;h3&gt;Empty Starts and Stops&lt;/h3&gt;<a name="line.134"></a>
<span class="sourceLineNo">135</span> *<a name="line.135"></a>
<span class="sourceLineNo">136</span> * &lt;p&gt;<a name="line.136"></a>
<span class="sourceLineNo">137</span> * An "empty start" occurs when an instance is {@linkplain #start started} but the persistent XML file is either missing,<a name="line.137"></a>
<span class="sourceLineNo">138</span> * does not validate, or cannot be read for some other reason. In such cases, the instance will start with no object graph,<a name="line.138"></a>
<span class="sourceLineNo">139</span> * and {@link #getRoot} will return null. This situation will correct itself as soon as the object graph is written via<a name="line.139"></a>
<span class="sourceLineNo">140</span> * {@link #setRoot setRoot()} or the persistent file appears (effecting an "out-of-band" update). At that time, {@linkplain<a name="line.140"></a>
<span class="sourceLineNo">141</span> * #addListener listeners} will be notified for the first time, with {@link PersistentObjectEvent#getOldRoot} returning null.<a name="line.141"></a>
<span class="sourceLineNo">142</span> * &lt;/p&gt;<a name="line.142"></a>
<span class="sourceLineNo">143</span> *<a name="line.143"></a>
<span class="sourceLineNo">144</span> * &lt;p&gt;<a name="line.144"></a>
<span class="sourceLineNo">145</span> * Whether empty starts are allowed is determined by the {@link #isAllowEmptyStart allowEmptyStart} property (default<a name="line.145"></a>
<span class="sourceLineNo">146</span> * {@code false}). When empty starts are disallowed and the persistent XML file cannot be successfully read,<a name="line.146"></a>
<span class="sourceLineNo">147</span> * then {@link #start} will instead throw an immediate {@link PersistentObjectException}.<a name="line.147"></a>
<span class="sourceLineNo">148</span> * &lt;/p&gt;<a name="line.148"></a>
<span class="sourceLineNo">149</span> *<a name="line.149"></a>
<span class="sourceLineNo">150</span> * &lt;p&gt;<a name="line.150"></a>
<span class="sourceLineNo">151</span> * Similarly, "empty stops" are allowed when the {@link #isAllowEmptyStop allowEmptyStop} property is set to {@code true}<a name="line.151"></a>
<span class="sourceLineNo">152</span> * (by default it is {@code false}). An "empty stop" occurs when a null value is passed to {@link #setRoot setRoot()}<a name="line.152"></a>
<span class="sourceLineNo">153</span> * (note, an invalid XML file appearing on disk does not cause an empty start).<a name="line.153"></a>
<span class="sourceLineNo">154</span> * Subsequent invocations of {@link #getRoot} will return {@code null}. The persistent file is &lt;b&gt;not&lt;/b&gt;<a name="line.154"></a>
<span class="sourceLineNo">155</span> * modified when null is passed to {@link #setRoot}. When empty stops are disallowed, then invoking<a name="line.155"></a>
<span class="sourceLineNo">156</span> * {@link #setRoot} with a {@code null} object will result in an {@link IllegalArgumentException}.<a name="line.156"></a>
<span class="sourceLineNo">157</span> * &lt;/p&gt;<a name="line.157"></a>
<span class="sourceLineNo">158</span> *<a name="line.158"></a>
<span class="sourceLineNo">159</span> * &lt;p&gt;<a name="line.159"></a>
<span class="sourceLineNo">160</span> * Allowing empty starts and/or stops essentially creates an "unconfigured" state represented by a null root object.<a name="line.160"></a>
<span class="sourceLineNo">161</span> * When empty starts and empty stops are both disallowed, there is no "unconfigured" state: once started, {@link #getRoot}<a name="line.161"></a>
<span class="sourceLineNo">162</span> * can be relied upon to always return a non-null, validated root object.<a name="line.162"></a>
<span class="sourceLineNo">163</span> * &lt;/p&gt;<a name="line.163"></a>
<span class="sourceLineNo">164</span> *<a name="line.164"></a>
<span class="sourceLineNo">165</span> * &lt;p&gt;<a name="line.165"></a>
<span class="sourceLineNo">166</span> * See {@link AbstractConfiguredBean} for a useful superclass that automatically handles starting and stopping<a name="line.166"></a>
<span class="sourceLineNo">167</span> * based on the state of an associated {@link PersistentObject}.<a name="line.167"></a>
<span class="sourceLineNo">168</span> * &lt;/p&gt;<a name="line.168"></a>
<span class="sourceLineNo">169</span> *<a name="line.169"></a>
<span class="sourceLineNo">170</span> * &lt;h3&gt;Shared Roots&lt;/h3&gt;<a name="line.170"></a>
<span class="sourceLineNo">171</span> *<a name="line.171"></a>
<span class="sourceLineNo">172</span> * Each time {@link #setRoot setRoot()} or {@link #getRoot getRoot()} is invoked, a deep copy of the root object<a name="line.172"></a>
<span class="sourceLineNo">173</span> * is made. This prevents external code from changing any node in the "official" object graph held by this instance,<a name="line.173"></a>
<span class="sourceLineNo">174</span> * and allows invokers of {@link #getRoot getRoot()} to modify to the returned object graph without affecting other invokers.<a name="line.174"></a>
<span class="sourceLineNo">175</span> * However, there may be cases where this deep copy is an expensive operation in terms of time or memory.<a name="line.175"></a>
<span class="sourceLineNo">176</span> * The {@link #getSharedRoot getSharedRoot()} method can be used in these situations. This method returns the same<a name="line.176"></a>
<span class="sourceLineNo">177</span> * root object each time it is invoked (this shared root is itself a deep copy of the "official" root). Therefore, only<a name="line.177"></a>
<span class="sourceLineNo">178</span> * the very first invocation pays the price of a copy. However, all invokers of {@link #getSharedRoot getSharedRoot()}<a name="line.178"></a>
<span class="sourceLineNo">179</span> * must treat the object graph as read-only to avoid each other seeing unexpected changes.<a name="line.179"></a>
<span class="sourceLineNo">180</span> * &lt;/p&gt;<a name="line.180"></a>
<span class="sourceLineNo">181</span> *<a name="line.181"></a>
<span class="sourceLineNo">182</span> * &lt;h3&gt;Delegate Function&lt;/h3&gt;<a name="line.182"></a>
<span class="sourceLineNo">183</span> *<a name="line.183"></a>
<span class="sourceLineNo">184</span> * &lt;p&gt;<a name="line.184"></a>
<span class="sourceLineNo">185</span> * Instances must be configured with a {@link PersistentObjectDelegate} that knows how to validate the object graph<a name="line.185"></a>
<span class="sourceLineNo">186</span> * and perform conversions to and from XML. See {@link PersistentObjectDelegate} and its implementations for details.<a name="line.186"></a>
<span class="sourceLineNo">187</span> * &lt;/p&gt;<a name="line.187"></a>
<span class="sourceLineNo">188</span> *<a name="line.188"></a>
<span class="sourceLineNo">189</span> * &lt;h3&gt;Schema Changes&lt;/h3&gt;<a name="line.189"></a>
<span class="sourceLineNo">190</span> *<a name="line.190"></a>
<span class="sourceLineNo">191</span> * &lt;p&gt;<a name="line.191"></a>
<span class="sourceLineNo">192</span> * Like any database, the XML schema may evolve over time. The {@link PersistentObjectSchemaUpdater} class provides a simple<a name="line.192"></a>
<span class="sourceLineNo">193</span> * way to apply and manage schema updates using XSLT transforms.<a name="line.193"></a>
<span class="sourceLineNo">194</span> * &lt;/p&gt;<a name="line.194"></a>
<span class="sourceLineNo">195</span> *<a name="line.195"></a>
<span class="sourceLineNo">196</span> * &lt;h3&gt;Transaction Manager&lt;/h3&gt;<a name="line.196"></a>
<span class="sourceLineNo">197</span> *<a name="line.197"></a>
<span class="sourceLineNo">198</span> * &lt;p&gt;<a name="line.198"></a>
<span class="sourceLineNo">199</span> * If using Spring, consider using a {@link PersistentObjectTransactionManager} for transactional access to a<a name="line.199"></a>
<span class="sourceLineNo">200</span> * {@link PersistentObject}.<a name="line.200"></a>
<span class="sourceLineNo">201</span> * &lt;/p&gt;<a name="line.201"></a>
<span class="sourceLineNo">202</span> *<a name="line.202"></a>
<span class="sourceLineNo">203</span> * @param &lt;T&gt; type of the root object<a name="line.203"></a>
<span class="sourceLineNo">204</span> * @see PersistentObjectDelegate<a name="line.204"></a>
<span class="sourceLineNo">205</span> * @see PersistentObjectSchemaUpdater<a name="line.205"></a>
<span class="sourceLineNo">206</span> * @see PersistentObjectTransactionManager<a name="line.206"></a>
<span class="sourceLineNo">207</span> * @see AbstractConfiguredBean<a name="line.207"></a>
<span class="sourceLineNo">208</span> */<a name="line.208"></a>
<span class="sourceLineNo">209</span>public class PersistentObject&lt;T&gt; {<a name="line.209"></a>
<span class="sourceLineNo">210</span><a name="line.210"></a>
<span class="sourceLineNo">211</span>    private static final long EXECUTOR_SHUTDOWN_TIMEOUT = 1000;             // 1 second<a name="line.211"></a>
<span class="sourceLineNo">212</span><a name="line.212"></a>
<span class="sourceLineNo">213</span>    protected final Logger log = LoggerFactory.getLogger(this.getClass());<a name="line.213"></a>
<span class="sourceLineNo">214</span><a name="line.214"></a>
<span class="sourceLineNo">215</span>    private final HashSet&lt;PersistentObjectListener&lt;T&gt;&gt; listeners = new HashSet&lt;PersistentObjectListener&lt;T&gt;&gt;();<a name="line.215"></a>
<span class="sourceLineNo">216</span><a name="line.216"></a>
<span class="sourceLineNo">217</span>    private PersistentObjectDelegate&lt;T&gt; delegate;<a name="line.217"></a>
<span class="sourceLineNo">218</span>    private FileStreamRepository streamRepository;<a name="line.218"></a>
<span class="sourceLineNo">219</span>    private long writeDelay;<a name="line.219"></a>
<span class="sourceLineNo">220</span>    private long checkInterval;<a name="line.220"></a>
<span class="sourceLineNo">221</span><a name="line.221"></a>
<span class="sourceLineNo">222</span>    private T root;                                         // current root object (private)<a name="line.222"></a>
<span class="sourceLineNo">223</span>    private T sharedRoot;                                   // current root object (shared)<a name="line.223"></a>
<span class="sourceLineNo">224</span>    private T writebackRoot;                                // pending persistent file writeback value<a name="line.224"></a>
<span class="sourceLineNo">225</span>    private ScheduledExecutorService scheduledExecutor;     // used for file checking and delayed write-back<a name="line.225"></a>
<span class="sourceLineNo">226</span>    private ExecutorService notifyExecutor;                 // used to notify listeners<a name="line.226"></a>
<span class="sourceLineNo">227</span>    private ScheduledFuture&lt;?&gt; pendingWrite;                // a pending delayed write-back<a name="line.227"></a>
<span class="sourceLineNo">228</span>    private long version;                                   // current root object version<a name="line.228"></a>
<span class="sourceLineNo">229</span>    private long timestamp;                                 // timestamp of persistent file when we last read it<a name="line.229"></a>
<span class="sourceLineNo">230</span>    private boolean allowEmptyStart;<a name="line.230"></a>
<span class="sourceLineNo">231</span>    private boolean allowEmptyStop;<a name="line.231"></a>
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<span class="sourceLineNo">235</span>     * Constructor.<a name="line.235"></a>
<span class="sourceLineNo">236</span>     *<a name="line.236"></a>
<span class="sourceLineNo">237</span>     * &lt;p&gt;<a name="line.237"></a>
<span class="sourceLineNo">238</span>     * The {@code writeDelay} is the maximum delay after an update operation before a write-back to the persistent file<a name="line.238"></a>
<span class="sourceLineNo">239</span>     * must be initiated.<a name="line.239"></a>
<span class="sourceLineNo">240</span>     *<a name="line.240"></a>
<span class="sourceLineNo">241</span>     * @param delegate delegate supplying required operations<a name="line.241"></a>
<span class="sourceLineNo">242</span>     * @param file the file used to persist<a name="line.242"></a>
<span class="sourceLineNo">243</span>     * @param writeDelay write delay in milliseconds, or zero for immediate write-back<a name="line.243"></a>
<span class="sourceLineNo">244</span>     * @param checkInterval check interval in milliseconds, or zero to disable persistent file checks<a name="line.244"></a>
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<span class="sourceLineNo">246</span>     * @throws IllegalArgumentException if {@code writeDelay} or {@code checkInterval} is negative<a name="line.246"></a>
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<span class="sourceLineNo">249</span>        this.setDelegate(delegate);<a name="line.249"></a>
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<span class="sourceLineNo">254</span><a name="line.254"></a>
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<span class="sourceLineNo">256</span>     * Simplified constructor configuring for immediate write-back and no persistent file checks.<a name="line.256"></a>
<span class="sourceLineNo">257</span>     *<a name="line.257"></a>
<span class="sourceLineNo">258</span>     * &lt;p&gt;<a name="line.258"></a>
<span class="sourceLineNo">259</span>     * Equivalent to:<a name="line.259"></a>
<span class="sourceLineNo">260</span>     * &lt;blockquote&gt;&lt;code&gt;<a name="line.260"></a>
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<span class="sourceLineNo">262</span>     * &lt;/code&gt;&lt;/blockquote&gt;<a name="line.262"></a>
<span class="sourceLineNo">263</span>     */<a name="line.263"></a>
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<span class="sourceLineNo">275</span>     * Get the configured {@link PersistentObjectDelegate}.<a name="line.275"></a>
<span class="sourceLineNo">276</span>     *<a name="line.276"></a>
<span class="sourceLineNo">277</span>     * @return the delegate supplying required operations<a name="line.277"></a>
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<span class="sourceLineNo">284</span>     * Configure the {@link PersistentObjectDelegate}.<a name="line.284"></a>
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<span class="sourceLineNo">286</span>     * @param delegate delegate supplying required operations<a name="line.286"></a>
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<span class="sourceLineNo">288</span>     * @throws IllegalStateException if this instance is started<a name="line.288"></a>
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<span class="sourceLineNo">299</span>     * Get the persistent file containing the XML form of the persisted object.<a name="line.299"></a>
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<span class="sourceLineNo">308</span>     * Set the persistent file containing the XML form of the persisted object.<a name="line.308"></a>
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<span class="sourceLineNo">312</span>     * @throws IllegalStateException if this instance is started<a name="line.312"></a>
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<span class="sourceLineNo">323</span>     * Get the maximum delay after an update operation before a write-back to the persistent file<a name="line.323"></a>
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<span class="sourceLineNo">325</span>     *<a name="line.325"></a>
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<span class="sourceLineNo">333</span>     * Set the maximum delay after an update operation before a write-back to the persistent file<a name="line.333"></a>
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<span class="sourceLineNo">389</span>     * &lt;p&gt;<a name="line.389"></a>
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<span class="sourceLineNo">392</span>     *<a name="line.392"></a>
<span class="sourceLineNo">393</span>     * &lt;p&gt;<a name="line.393"></a>
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<span class="sourceLineNo">396</span>     * &lt;p&gt;<a name="line.396"></a>
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<span class="sourceLineNo">1001</span>            this.checkFile();<a name="line.1001"></a>
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<span class="sourceLineNo">1046</span>            Thread.currentThread().interrupt();<a name="line.1046"></a>
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<span class="sourceLineNo">1052</span>// Convience reader &amp; writer<a name="line.1052"></a>
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<span class="sourceLineNo">1054</span>    /**<a name="line.1054"></a>
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<span class="sourceLineNo">1058</span>     * This is a convenience method that can be used for a one-time deserialization from an XML {@link Source} without having<a name="line.1058"></a>
<span class="sourceLineNo">1059</span>     * to go through the whole {@link PersistentObject} lifecycle.<a name="line.1059"></a>
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<span class="sourceLineNo">1065</span>     * @return deserialized root object, never null<a name="line.1065"></a>
<span class="sourceLineNo">1066</span>     * @throws IllegalArgumentException if any parameter is null<a name="line.1066"></a>
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<span class="sourceLineNo">1068</span>     * @throws PersistentObjectException if an error occurs<a name="line.1068"></a>
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<span class="sourceLineNo">1079</span>        T root;<a name="line.1079"></a>
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<span class="sourceLineNo">1104</span>     * &lt;p&gt;<a name="line.1104"></a>
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<span class="sourceLineNo">1106</span>     * opening and closing the given {@link File}.<a name="line.1106"></a>
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<span class="sourceLineNo">1116</span>     * @throws PersistentObjectException if an error occurs<a name="line.1116"></a>
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<span class="sourceLineNo">1234</span>            output.close();<a name="line.1234"></a>
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<span class="sourceLineNo">1241</span>     * Write a persistent object using the given delegate.<a name="line.1241"></a>
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<span class="sourceLineNo">1243</span>     * &lt;p&gt;<a name="line.1243"></a>
<span class="sourceLineNo">1244</span>     * This is a wrapper around {@link #write(Object, PersistentObjectDelegate, Result)}.<a name="line.1244"></a>
<span class="sourceLineNo">1245</span>     * &lt;/p&gt;<a name="line.1245"></a>
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<span class="sourceLineNo">1271</span>     * corresponding to the snapshot.<a name="line.1271"></a>
<span class="sourceLineNo">1272</span>     *<a name="line.1272"></a>
<span class="sourceLineNo">1273</span>     * @see PersistentObject#getRootSnapshot<a name="line.1273"></a>
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<span class="sourceLineNo">1276</span><a name="line.1276"></a>
<span class="sourceLineNo">1277</span>        private final T root;<a name="line.1277"></a>
<span class="sourceLineNo">1278</span>        private final long version;<a name="line.1278"></a>
<span class="sourceLineNo">1279</span><a name="line.1279"></a>
<span class="sourceLineNo">1280</span>        public Snapshot(T root, long version) {<a name="line.1280"></a>
<span class="sourceLineNo">1281</span>            this.root = root;<a name="line.1281"></a>
<span class="sourceLineNo">1282</span>            this.version = version;<a name="line.1282"></a>
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<span class="sourceLineNo">1284</span><a name="line.1284"></a>
<span class="sourceLineNo">1285</span>        /**<a name="line.1285"></a>
<span class="sourceLineNo">1286</span>         * Get the persistent root associated with this instance.<a name="line.1286"></a>
<span class="sourceLineNo">1287</span>         */<a name="line.1287"></a>
<span class="sourceLineNo">1288</span>        public T getRoot() {<a name="line.1288"></a>
<span class="sourceLineNo">1289</span>            return this.root;<a name="line.1289"></a>
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<span class="sourceLineNo">1291</span><a name="line.1291"></a>
<span class="sourceLineNo">1292</span>        /**<a name="line.1292"></a>
<span class="sourceLineNo">1293</span>         * Get the version number of the persistent root associated with this instance.<a name="line.1293"></a>
<span class="sourceLineNo">1294</span>         */<a name="line.1294"></a>
<span class="sourceLineNo">1295</span>        public long getVersion() {<a name="line.1295"></a>
<span class="sourceLineNo">1296</span>            return this.version;<a name="line.1296"></a>
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<span class="sourceLineNo">1298</span>    }<a name="line.1298"></a>
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<span class="sourceLineNo">1300</span><a name="line.1300"></a>




























































</pre>
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